1. Field of the Invention
The present invention relates to envelope machines and more particularly to such machines of the rotary type wherein the operations involved in the forming of envelopes are performed in a continuous manner by the passage of material from end-to-end of the machine in rolling contact with various instrumentalities thereof.
More particularly, the present invention is directed to that mechanical equipment in an envelope machine line which performs the function of applying gum or adhesive to designated areas of the envelope blank prior to flap folding.
2. Description of the Prior Art
The generally practiced prior art technique of applying gum to precisely designated areas of an envelope blank in transit through a rotary envelope machine is to print the gum onto the blank by a rotary image transfer means called a picker as the envelope blank passes between the picker carrying roll and a backing roll. U.S. Pat. No. 2,568,629 to V. E. Heywood is representative of the prior art as presently practiced.
Gum is applied to the picker print face from the surface of a rotating metering roll in the same manner as practiced by the rotogravure arts. A portion of the rotating meter roll periphery is immersed in a viscous, fluidized gum bath. A doctor blade skims the film adhering to the meter roll surface to leave a film of gum having a precisely graduated thickness remaining on the roll surface. Continued rotation of the meter roll past the doctor blade brings the doctored gum film into contact with the print face of the picker which, by viscous fluid adhesion, picks that portion of the film off the meter roll surface onto the picker print face.
As the picker roll continues rotation past tangency with the meter roll and into tangency with a backing roll, a register aligned envelope blank is drawn into the nip between the picker and backing roll where gum on the picker print face transfers to the envelope surface.
Prior art equipment to perform the aforedescribed gum transfer function includes such features as cam adjusters on the meter roll bearings to advance and retard the meter roll surface relative to a fixed position doctor blade. However, such adjustment of the meter roll centerline also skews the meter roll and the axis thereof relative to the picker roll axis. Consequently, the picker print surfaces, which are ground about the picker roll axis, cannot run in tangential alignment with the meter roll.
From another perspective, normal wear of machine components will create an unevenness of the picker print surfaces relative to the meter roll surface. Although the same metering roll bearing cams may be adjusted to correct misalignment of the meter roll surface relative to the picker print surface, such adjustments are made at the sacrifice of meter roll alignment with the doctor blade.
Other shortcomings of prior art gum box designs relate to the rheology and viscous fluid flow characteristics of the gum substance. For example, the gum solids are dissolved in a highly volatile solvent to permit rapid drying after application to the envelope blank. However, the gum pond through which the meter roll rotates is atmospherically open thereby permitting solvent loss to the atmosphere prior to application on the envelope. To minimize the surface area of fluid gum exposed by the gum pond, small containers of such gum are manually changed and positioned invertly over the gum pond for vacuum control of the pond level. Although it is desirable to minimize the pond size, the absolute scale required for manual manipulation of a gum supply container necessitates an undesirably large pond.
Furthermore, the continuous fluid shear of the meter roll surface through the pond tends to upset and thicken the gum viscosity. Another criticism of prior art gum boxes is the flow distribution of the gum from the centrally located bottle supply. Static gum pond regions in the side corners remote from the supply bottle and opposite from the metering roll permit the gum to dry, thicken and gel, a process which progressively obstructs the entire pond flow.
All of the foregoing deficiencies of prior art gum box designs collectively collaborate when a complete stoppage of the envelope machine occurs. Rotation of the meter roll is driven by direct gear engagement with the primary machine drive. Accordingly, when the machine stops, so too does the meter roll. When the meter roll stops, gum within the gum box begins to gel thereby necessitating a complete cleanout of the gum box.
It is therefore, an objective of the present invention to provide a gum box having individual adjustments for the doctor blade relative to the meter roll and the meter roll rotation axis relative to the picker roll axis.
Another object of the present invention is to eliminate the manually exchanged, inverted bottle supply reservoir for the gum pond.
Another object of the present invention is to reduce the volumetric size and exposed surface area of the gum pond.
Another object of the present invention is to maintain the gum box volume with pumped transfer from a totally enclosed, remotely located supply reservoir.
Another object of the present invention is to maintain a closely controlled liquid level of a low volume gum pond with non-contacting level control means.
Another object of the present invention is provision of auxiliary drive power for the meter roll which continues rotation of the meter roll after and during machine stoppage.
Another object of the present invention is provision of a mechanism to safely disengage the meter roll from the picker surface to prevent injury to either during a machine stoppage while the meter roll is driven by an auxiliary power supply.